This amp is special and very impressive, but I have not found any real discussion of what makes this little amp a true gem. So here are my thoughts and ideas.
The coupling of the speaker into the node made by ground, top of R1 (0,56R) and the source pin of the FET is a genius use of positive feedback to shape the character of the second harmonic distortion. It seems to add a great deal of "ooohmpfh!" to the little amp as evident by the following comment from Nelson Pass in the original article:
Even the measured distortion curves tend to indicate this use of positive feedback, where the amp behaves exceedingly well all the way to its limits set by the 1 ampere current and the 12 volt power supply.
I have found that some careful use of positive feedback adds both a very robust character and a sense of abundant power when driving difficult loads (normal multiway loudspeakers with crossovers), not easily explained by measured data (such as damping factor, THD, bandwidth etc). This was evident by my SLAPS amp build among several other.
The coupling of the speaker into the node made by ground, top of R1 (0,56R) and the source pin of the FET is a genius use of positive feedback to shape the character of the second harmonic distortion. It seems to add a great deal of "ooohmpfh!" to the little amp as evident by the following comment from Nelson Pass in the original article:
Even the measured distortion curves tend to indicate this use of positive feedback, where the amp behaves exceedingly well all the way to its limits set by the 1 ampere current and the 12 volt power supply.
I have found that some careful use of positive feedback adds both a very robust character and a sense of abundant power when driving difficult loads (normal multiway loudspeakers with crossovers), not easily explained by measured data (such as damping factor, THD, bandwidth etc). This was evident by my SLAPS amp build among several other.
I would describe this as the Mosfet being operated without degeneration
(by virtue of some positive fb if you like) and it also gives us maximal
open loop gain.
All told, this is not a wild and crazy circuit, just one that sounds quite
good with little effort. Remarkably it is still doing a very good job with
my 3 ohm 87 dB SR-1 speakers.
(by virtue of some positive fb if you like) and it also gives us maximal
open loop gain.
All told, this is not a wild and crazy circuit, just one that sounds quite
good with little effort. Remarkably it is still doing a very good job with
my 3 ohm 87 dB SR-1 speakers.
3 ohms? The Zenductor is the little amp that could. It is clapping it's little heart out!
I do listen at reasonable levels - no disco...
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Huh.... I read your write up on the El Pipos... didn't you guys blow up one of the woofers? Surely that wasn't done playing Bill Monroe or Buck Owens or Gregorian Chants in a 1000 year old church in the Pyrenees. 😉
Do you mean you are not listening to this amp at disco levels of have you stopped, ahem, cranking the likes of ZZ Top to live rock levels?
Short term, if I wanted to up the power, just a bit, would a beefier power supply do the trick? ( more volts, more amps...). I've been wondering what these babies might do with the Maggies. I don't expect full Magnepan bass, but the 35w SissySIT left me dumbfounded on the Maggie 1.7s.
BTW, I prefer how they sound with the gain just set one quarter of the way up. They do get louder, yes, but the sound loses its "you are there" quality. I really would prefer to keep the gain as it is but up the power supply, if it works.. and not melting the heat sink ( running at 78C ).
Do you mean you are not listening to this amp at disco levels of have you stopped, ahem, cranking the likes of ZZ Top to live rock levels?
Short term, if I wanted to up the power, just a bit, would a beefier power supply do the trick? ( more volts, more amps...). I've been wondering what these babies might do with the Maggies. I don't expect full Magnepan bass, but the 35w SissySIT left me dumbfounded on the Maggie 1.7s.
BTW, I prefer how they sound with the gain just set one quarter of the way up. They do get louder, yes, but the sound loses its "you are there" quality. I really would prefer to keep the gain as it is but up the power supply, if it works.. and not melting the heat sink ( running at 78C ).
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So, no go upping the volts on the Zenductor?you have some new, more potent, SissySIT?
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@Zen Mod As a matter of fact, yeah, the 252 SIT. I'm gonna call mine the MachoSIT.
Until the BigBaddaBoom is released... (Just got a matched quad set of Tokins THF-51S... so please don't take too long..).
The Iron Pre will be the BigBaddaBing for the BigBaddaBoom.
That will be the DiscoSIT setup. At that point I'll be able to get off your Soul Amp Train and happily return to the caboose where I will Go Around In SITrcles.
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@Nelson Pass Hey, I remember this... it was... hilarious.. every time I read it I end up ROTFLOL from you own write up... ( your writings are funny...)...
https://www.firstwatt.com/pdf/art_elpipeo.pdf
The Party Incident
The first listening sessions were run with 100 watt amplifiers. Of course something like El Pipe-O calls for monster amplifiers, so we acquired Pass X1000’s, which can do about 4,000 watts peak (per channel) into 4 ohms. The occasion of firing these up called for another party, during which we drank a lot of Cabernet and then decided to test the power handling claims of the woofer manufacturer. These claims were fairly accurate at 800 watts peak each, and at the end of this event we were down to two woofers
Now, you are in NorCal... down here in SoCal we drink sangria spiked with tequila to test our woofers... Whatever, the point is to have fun... good that I don't have something like an X1000 lying around... but I do have lots of wine. Mostly Pinot from the Central Coast.
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This reminds me of some highly scientific experiments in my early twenties involving a couple of friends, some cheap 8" car woofers, a bottle of moonshine and a 230V wall outlet.
You would need better heat sinks (a fan?). Here is a simulated version with 19 volts and 1,65 Amps from the powersupply. The mosfet dissipates 28,4 watts of heat, and the amp seems to hit 1.1 procent simulated THD at 6.6 watts (8 Ohm load). And it seems to hit about 10 watts at the first onset of (very soft and gradual) clipping.
Attachments
Would the bias setting be higher then? Right now it's at 500mV. I imagine the gain setting is a ratio so it would not need adjustments.
The other possibility would be to move the mosfet to an external, larger heat sink. would some 12 gauge wires solid wires be good for this? Stranded?
The other possibility would be to move the mosfet to an external, larger heat sink. would some 12 gauge wires solid wires be good for this? Stranded?
I wouldn't do 12awg. Something like 16awg would be much more than enough and easier to work with. You can even use a small wire for the gate like 23awg or something like that.
I've been thinking of buying a lab power supply...
https://www.amazon.com/Siglent-Tech...4&sprefix=power+supply+siglent,aps,168&sr=8-5
or
https://www.amazon.com/Siglent-Tech.../dp/B01410O424/ref=psdc_1161760_t1_B01HENYNZS
Would these be overkill?
I might also get a scope and a signal/function generator.
To be honest, the last time I was looking at scopes, signal generators, programmable power supplies, etc ( mostly HP and Tektronix ) they cost thousands of dollars.
https://www.amazon.com/Siglent-Tech...4&sprefix=power+supply+siglent,aps,168&sr=8-5
or
https://www.amazon.com/Siglent-Tech.../dp/B01410O424/ref=psdc_1161760_t1_B01HENYNZS
Would these be overkill?
I might also get a scope and a signal/function generator.
To be honest, the last time I was looking at scopes, signal generators, programmable power supplies, etc ( mostly HP and Tektronix ) they cost thousands of dollars.
Those lab power supplies (with big displays) are expensive and overkill if you already have a couple good DMMs. Simpler supplies and a few DMMs are a more versatile combination.
Thrilled to see that a 10W version can be made with a widely available 19V power supply.
I really don't understand what you're trying to achieve! The first watt matters!
In my eyes it's a contradiction, such a pretty single-stage amplifier with as much power as possible!
In my eyes it's a contradiction, such a pretty single-stage amplifier with as much power as possible!